1. Technical Field
The present invention generally relates to fuel control systems for fuel-injected vehicles and, more particularly, to a fuel injector system using fuel vapors from the fuel tank to power an internal combustion engine during start-up and steady-state operation.
2. Discussion
Modern automotive vehicle engines commonly employ injected fuel for combustion. At start-up, when the engine is not fully warm, the injected fuel is commonly cold. Cold fuel is harder to vaporize than warm fuel. As such, some of the fuel remains in a liquid state when injected. The injected liquid fuel tends to lead to decreased combustibility at start-up. This may result in undesirable emission levels.
To improve emission levels, different techniques have been employed before and after combustion. One pre-combustion treatment has been to heat the fuel prior to its injection. By heating the fuel, it becomes more easily vaporized thereby improving its combustibility. While successful, such pre-combustion heating is complex and expensive to implement. A common post-combustion treatment involves the employment of a catalyst in the engine exhaust gas stream. The catalyst burns the undesirable exhaust gas constituents prior to their passage to the atmosphere. While also successful, such post-combustion burning is also expensive and complex to implement.
Modern automotive vehicles are commonly equipped with a fuel vapor purge control system. Such a system accommodates fuel within the fuel tank which tends to vaporize as temperatures increase. The vaporized fuel collects in the fuel tank and is periodically removed by the purge vapor control system. The fuel vapors from the tank are initially collected and stored in a vapor canister. When the engine operating conditions are conducive to purging, a purge valve is opened permitting the engine to draw the fuel vapors from the purge canister for combustion.
Even with such a purge fuel vapor control system installed, some fuel vapor is commonly present in the dome portion of the fuel tank at start-up. Advantageously, it has now been discovered that these fuel vapors can be supplied to the engine at start-up via the fuel injectors. This allows the engine to utile fuel vapors in place of some portion of the cold liquid fuel at start-up. Moreover, the fuel vapors can continue to be injected during the steady-state operation to take full advantage of the availability of the fuel vapor.